Therapeutic and diagnostic medical procedures utilize equipment capable of processing electrical signals or electrical currents that are received from the body of a patient or are delivered to the patient's body. In these procedures, the interface between the patient's skin and the applicable equipment typically includes a biomedical electrode constructed to include a conductor connected electrically to the medical equipment and a conductive medium that is adapted for contact with the patient's skin (e.g., with an adhesive).
By way of example, biomedical electrodes are employed in therapeutic procedures and equipment such as in transcutaneous electronic nerve stimulation (TENS) devices that are used for pain management; neuromuscular stimulation (NMS) techniques for the treatment of certain conditions such as scoliosis; defibrillation electrodes for dispensing electrical energy to a patient's chest cavity to defibrillate the heart; and dispersive electrodes that receive electrical energy that has been applied to an incision made during electrosurgery. Biomedical electrodes are also employed in diagnostic procedures and equipment that include electrocardiography for monitoring heart activity and diagnosing heart abnormalities.
Non-polarizable electrodes, and in particular electrodes made with silver and/or silver chloride are highly stable and have been widely used in diagnostic applications. In low-cost versions, these electrodes are often coated in thin sections of conductive ink on an insulating backing. Conductive inks formulated for these applications typically include silver/silver chloride particles and a polymeric binder. A conducting adhesive (e.g., a hydrogel or hydrocolloid) is laminated to the silver-coated backing, and the assembly is die cut to the required electrode shape. The conductive adhesive serves the dual purpose of providing adhesion of the electrode to the skin as well as permitting electrical transduction of the electrical activity of the heart. The adhesive layer of the electrodes are protected with a release liner prior to the application of the electrode to the skin.
The monolithic adhesive construction of typical non-polarizable electrodes has been problematic because of an exposed edge of adhesive along the perimeter of the electrode. The ionically conductive phase of the adhesive consists of an alkali or alkaline earth metal chloride (typically potassium or sodium chloride) dissolved in water with an optional humectant added to slow down evaporative loss. However, under low humidity conditions (which can be as low as 20% R.H in hospitals), rapid evaporative loss of water occurs along with an accompanying degradation of the electrical properties of the electrode. The electrical properties are related to the conductance of dissolved salt in the water/humectant mixture of the adhesive. As water evaporates, the humectant concentration increases. Because alkali and alkaline earth halides are poorly soluble in commonly used humectants, the ionic concentration of the adhesive is compromised and the electrical properties degrade.
There is a need for improved conductive adhesives and for articles comprising such adhesives including biomedical articles such as biomedical electrodes, for example.